Program. t-stats for home w/ dual systems

[muggy]

This may be a stupid question, for which I'll apologize right up front.

I live in Houston, and recently bought a 2-story home with separate upstairs and downstairs systems. The equipment is all fine (~9yr old Trane A/C & gas heat, inspected & maintained), but we're always either hot or cold because the two thermostats are hard to get set "right". This is partly because of the coarse temp scale and apparent wide deadband (?) that the existing t-stats (Honeywell mercury-switch types) have, but also because we have a large open atrium between the upstairs and downstairs, and both t-stats are located near it. So if the downstairs t-stat is set a little high when the heat is running, the upstairs t-stat stays warm and the upstairs heat doesn't come on... so the upstairs bedrooms stay cold. When the AC is running and the t-stats are a little "off", we have the opposite problem... cool upstairs, but hot in the downstairs living areas b/c the downstairs t-stat senses cooler air settling in the atrium, so the downstairs a/c doesn't run enough.

All this just means that it takes a little time (sometimes a few days) to get both t-stats set where they need to be. Then everything's great... unless we have to switch from heat to cool... in which case both t-stats have to be adjusted down, and it takes another day or two to get 'em right. From November to March, we're changing from heat to cool and back pretty often... sometimes several times a week... so it's rarely comfortable in the house.

Anyway, enough of the boring homeowner babble. I'd like to just put in a pair of programmable setback thermostats with auto heat/cool changeover - but I'm afraid that they might "work against each other"... upstairs cooling, downstairs heating, and both running all the time. So finally, my real questions:
- Is this something that's likely to be a problem?
- Are there any programmable t-stats out there that can control my two separate systems, but that will "talk" to each other so that they're either both on cool or both on heat?
- Is there some way to use a zone control unit to take the input from both thermostats, and have the it control the two systems "intelligently"?
- Or should I just forget about auto changeover?

Much thanks in advance.

[Advanced Response]

Sounds like one or both themostats are in bad locations and would be best to be moved to a better location for more accurate temp readings..
I would contact some local hvac contractors for some suggestions about possible better locations for one or both of the thermostats.. If a one of my customers is interested in having a thermostat moved, I ask if they would like to test drive a differant location.. I know you are wondering how.. I carry a used wireless thermostat just to let the customer borrow(pre-paid fee) that I have a strap on that the customer just needs a nail in the wall and can play around with trying to find the best place to relocate the thermostat to.. This has been proven very reliable, but the best relocation of the thermostat is usually where I reccommend but it gives the customer some piece of mind that the new location will work better that the original location..

Just have to love the wireless technology.. Now if the wireless thermostats were just more durable,, then I wouldn't have to run that wire.. I like the wireless technology but it is not as durable as TV remotes or many other wireless products yet.. But, I like using it as a tool for my customers satisfaction.. I guess I kinda lucked into this because I got my wireless t-stat from a customer that just had to have one but then when he got it,, he stated that it never was where he wanted it and that resulted in unfavorable house temps swings..

Good luck
J

[BaldLoonie]

I'm with AR, get the upstairs stat in your bedroom suite. Could cause the hall and atrium to run warm but at least your bedrooms will be comfy. I would be a little nervous about autochangeover, you're right, could be cases where downstairs heat causes upstairs cool to come on.

[pipedope]

i also agree with AR. 1)try running the fans on both t-stat to on 2) do not use the auto feature if you run a/c in below 60 degree weather you can ruin your compressors unless they are equiped with low ambient protection.

[muggy]

Thanks everyone for the good advice. I agree that the locations of the exising thermostats isn't the best... at least as far as u/s d/s temperature control goes. BUT, the rooms that are open to the "offending" atrium are where we spend most of our waking hours, so I'm hesitant to control the temperature strictly from thermostats that are distant from there.

Would you consider leaving them in the current locations (near atrium... which is bad, but in our most frequented space... which might be good) and adding a remote sensor for both the upstairs (in master bedroom) and downstairs (opposite end of the living area)?? Or would you advise just moving them?

Am I correct in guessing that none of the controls manufacturers is offering some kind of magic bullet for this situation... a multiple thermostat "unified controller" of some sort that is designed to control dual systems in some sort of coordinated manner? Basically a zone controller but with two AC units and no dampers?

And, if it's not against the rules... is there anybody in particular (hvac contractor) you guys would recommend in Houston?

Thanks again.
Jeff E.

[muggy]

Assuming there's nothing that will intelligently control these two separate systems, and make sure they both switch from heat to cool at the same time...

Could a thermostat with adjustable changeover deadband be used upstairs and downstairs - with deadband set fairly wide. I notice several stats that allow the same heat/cool setpoint, but with adjustable deadband:

Robertshaw 9701i, Totaline P374-1100FM, and Honeywell VisionPro. And I think they all support remote sensors and temperature averaging (for the bedroom) also. Would this work, or is simply relocating the thermostats a better idea?

Is there one of these that you guys would recommend over the others?

Also still looking for recommendations for a good HVAC contractor in the Houston area.

Much thanks.